Acetobromomaltose, a New Source of Carbohydrate Radicals. EPR Characterisation of Maltosyl and 2-Deoxymaltos-2-yl Radicals and Syntheses of Tetrasaccharide-like Mimics, Maltal, 3-α-Maltosyl Propiononitrile, 1,5-Anhydromaltitol and 2-Deoxymaltopyranoside

The acetoxy-protected maltosyl radical 1, obtained through bromine abstraction from acetobromomaltose (ABM), was studied by means of EPR spectroscopy. At room temperature, only the spectrum of 1 was observed, but at higher temperatures a second radical, the acetoxy-protected 2-deoxymaltos-2-yl radical 2, was detected, resulting from migration of an acetoxy group from position 2 to position 1. Some acetoxy-protected maltose derivatives were prepared from ABM, via different radical pathways involving 1 and 2 as intermediates. Electroreduction on silver provides tetrasaccharide-like mimics 7 and maltal 8. Photochemical generation of 1, followed by trapping with tributyltinhydride or with acrylonitrile, leads respectively to 1,5-anhydromaltitol 9 and to 3-α-maltosyl propiononitrile 10. Generation of 2 at 80°C by 1→2 isomerisation, followed by trapping with tributyltinhydride, leads to 2-deoxymaltopyranoside 11.